Comment by JKCalhoun
The long Discovery space craft depicted in the latter half of "2001: A Space Odyssey" was derived from the nuclear rocket. It was suggested that the radioactive part of an Orion-style space craft be put far away from the crew compartment.
We can probably can thank Fred Ordway (Marshall Spaceflight Center engineer) who Kubrick brought on board as technical consultant back then. (And of course for the look of the ships that are still so iconic over 50 years later I shouldn't leave off Harry Lange.)
The 2001 spacecraft was implied to be a NERVA-type nuclear rocket (ie push working fluid through a high temperature reactor), rather than an Orion type (propulsion via small nuclear explosions).
But yeah, "crew module, long thing, engine" was how these were, virtually always, depicted in sci-fi.